JPS6395853A - Multiple output switching regulator - Google Patents

Abstract

PURPOSE:To prevent an error action when the power source of a device is OFF, by detecting the interruption of an input power source, and by discharging the electric charge of the smoothing condenser of one of a plurality of outputs forcibly by the use of output of said detection. CONSTITUTION:So far as a multiple output switching regulator is concerned, rectified and smoothed direct current is ON/OFF-controlled by a switching transistor Q1 via a transistor T1, and from the secondary winding of the transistor T1, a plurality of rectified and smoothed DC outputs 1-2 obtained. In this case, a detection circuit 3 for detecting the interruption of an input AC power source 1, and a discharge circuit 4 for discharging the electric charge of a smoothing condenser C4 for the output 1 are added. The detection circuit 3 is composed of the LED of a photocoupler PC and the like, and the discharge circuit 4 is composed of the phototransistor of the PC, a discharging transistor Q2, and the like. Then, the fall of the output 1 can be made quicker when a power switch S1 is OFF, and the error action of a device can be prevented.

Description

Detailed Description of the Invention (Technical Field) The present invention turns on current flowing through a primary winding of a transformer having a plurality of secondary windings using a switching element.

The voltage induced in each secondary winding is rectified and smoothed to obtain a plurality of DC outputs, and one of the plurality of DC outputs is compared with a reference value to determine the on/off ratio of the switching element. This invention relates to a multi-output switching regulator that obtains multiple stable outputs by controlling.

(Prior Art) First, a conventional multi-output switching regulator will be described with reference to FIG.

AC power l to diode bridge DB, capacitor C
The DC output rectified and smoothed in step 3 is sent to the converter transformer T.
, Volume 1! Connected to one end of n+. Similarly, the other end of the primary winding n1 is connected to the other end of the DC output via a switching transistor Q1. This switching transistor Q is controlled by a pulse transformer T! by a signal from a control section 2, which will be described later. On appropriate via.

By intermittent switching at the off-ratio, an induced voltage is generated in each secondary winding of the transformer T. By rectifying and smoothing this induced voltage, multiple DC outputs are obtained.

In this example, in order to obtain two independent outputs (output 1 and output 2), two secondary windings ng+n3 are provided, and each
The next @ line has a rectifier diode, Dt l D4,
Commutation diode, D310i % smoothing choke coil L1. L! , smoothing capacitor Ca, Ch,
Resistors R4 and R1 are provided for voltage control during snack loading.

Further, the output voltage and voltage of the output 2 are fed back to the control section 2. The control unit 2 includes an error amplifier, an oscillation circuit, a reference voltage generation circuit, an output logic circuit, an output circuit, etc., and compares the output of the output 2 with a reference value, and the on/off ratio varies depending on the difference, and the oscillation Outputs pulses with a constant frequency determined by the circuit. This pulse is amplified within the control unit 2, and is passed through the pulse transformer Tz to the switching transistors Q,
to drive. When the output of output 2 is about to decrease due to input voltage, load fluctuation, etc., the control unit 2 turns it on.

A drive signal with a large off-ratio is generated, and as a result, the on/off ratio of the switching transistor Ql is also large, preventing a drop in the output, and vice versa.
The output voltage of is stabilized with high precision.

On the other hand, although there is no stabilizing operation due to feedback in the output 1, a substantially stabilized output voltage can be obtained due to the cross regulation effect of the transformer T1.

In the example in Figure 2, there is one approximately stabilized output, but two
3 outputs, 4 outputs by adding the next winding, rectifying and smoothing circuit, etc.
Output is also easily achievable.

A power supply configured in this way can be much smaller and cost-effective compared to a conventional dropper-type power supply that uses a transformer to step down the commercial power supply and perform rectification, smoothing, and stabilization. The frequency is increasing. In particular, it is suitable for power supplies for OA equipment such as copying machines that require high-precision power supplies for sequence and process control, and for motors, clutches, solenoids, counters, and high-voltage power supplies that do not require relatively high precision but require high capacity. Is this trend remarkable? j [In the example of a photographic machine, the output 2 supplies power to the control unit consisting of a microcomputer, LSI, IC, I-transistor, motors that drive the photoreceptor, optical system, etc., clutch, solenoid, high-pressure generator, etc. The output 1 that supplies power to the copying machine constitutes a power supply for the copying machine.

Since the load on the output 2 of the control unit power supply is almost constant no matter what state the copying machine is in, the control unit 2 of the IT source is mainly designed to prevent the output from fluctuating due to input voltage fluctuations. , the on/off ratio of the switching transistor Q is changed to stabilize the output.

On the other hand, as mentioned above, the power supply for driving output 1 is stabilized against input fluctuations in the same way as output 2, and furthermore, the power supply for driving output 1 is stabilized against input fluctuations, and
Since the area before the primary winding of 1 is stabilized by the cross regulation effect of the transformer, it is only affected by load fluctuations after the secondary winding. Therefore, although it is inferior to the output 2, sufficient stabilization for driving can be obtained, making it possible to significantly reduce the size and cost compared to the conventional one-dropper type.

However, even such a multi-output switching regulator has the following drawbacks.

Now, let us consider a case where the power switch sI is turned off with no load current flowing through the output 1 and the output 2 being under almost the rated load condition.

In the case of a copying machine, this is often the case when the copying machine is not in the process of copying but is on standby.

When the input voltage is turned off and the voltage across C0 falls below a certain value, control of the control unit 2 becomes impossible, and the outputs of the output 11 and the output 2 begin to decrease. Since a constant load is connected to output 2, the output starts to decrease rapidly compared to output 1. Since output 1 is almost in a no-load state, it decreases more gently to 6 than output 2. Therefore, even if the output voltage of output 2 drops below the operable voltage of the circuit connected to it, output 1 often maintains a value that is sufficient to drive the load. This situation is shown in No. 3 Kaizan).

The fact that sufficient voltage remains at output 1 to drive the load when output 2 makes it difficult for the circuit to operate normally indicates the possibility that an erroneous signal will be generated and malfunction will occur as a result. That is,
When the power switch of a copying machine or the like is turned off, there is a risk that the copy counter may erroneously advance or some copy sheets may be partially fed. To prevent this, it is necessary to make the output 2 smoothing capacitors C, C, larger than necessary, or to make the value of the dummy resistor R4 smaller than necessary, which hinders miniaturization and cost reduction. was.

(Objective) The object of the present invention is to solve such drawbacks, to make the unnecessary fall of the output steep when the power switch is turned off,
The purpose is to prevent malfunctions of equipment that uses this power supply.

(Configuration) Therefore, the present invention detects that the input power supply is cut off, and uses this signal to forcibly discharge the charge in the smoothing capacitor of at least one of the plurality of outputs. achieve.

An embodiment of the present invention will be described below with reference to FIG. Note that the same parts as in the conventional example are given the same reference numerals.

In this embodiment, an input power supply cutoff detection circuit 3 that detects cutoff of input AC power supply, and a smoothing capacitor C for output 1 are used.
A discharge circuit 4 for discharging the electric charge of J is added to the conventional example.

The input power supply cutoff detection circuit 3 includes a resistor R11l R1! that divides the voltage of the input AC power supply. , a diode D that rectifies and smoothes this, a capacitor C0, and a photocoupler PC LE.
D and a protection diode D1□.

When the power switch Sl is on, the input AC power is R11, R1! After being divided by and rectified by Dll, C
It is smoothed slightly by 8 and turns on the LED of the PC via R11. When S is turned off, the charge on C8 becomes R+t-P
It is immediately discharged by the C LED. Therefore PC LF
D turns on and off in synchronization with the power switch SI, so
An input power cutoff detection signal will be generated.

Next, the discharge circuit 4 will be explained. In this circuit, the collector of the phototransistor of the PC explained earlier is connected to the resistor R
The emitter is connected to the ■ side of the output 1 via 7, and the emitter is connected to the e side. Also, the connection point between the PC collector and R1 is
It is connected to the base of the discharge transistor Q2, and the base is connected to the e side of the output 1 via a resistor R. Q again! The collector of is connected to the e side of the output 1 via a resistor Rs.

With the above configuration, when the LED of the PC is on and the phototransistor is on, the base of C2 becomes low, so C2 is off. On the other hand, LED
When Q is off, Q is on. Therefore, when SI is on, C8 is off, and when SI is off, Q! turns on, the charge on C1 is rapidly discharged via R3.

On the other hand, output 2 is input AC 1! A constant output is obtained until the potential across the capacitor CI that rectifies and smoothes the source reaches a predetermined value, so when the power switch S1 is turned off, the fall of output 1 can be made faster, as described in the conventional example. No inconvenience will occur.

This situation is shown in FIG. 3. FIG. 3 (Ta) shows the present embodiment, and Okayama) shows the conventional example.

In the case of conventional example (b), S is turned off and C8 is turned off after (t,).
Until both ends of Ctt reach a predetermined value, output 1.2 outputs the rated output, but after tt it becomes uncontrollable and begins to decline, but when output 1 is almost no load, the attenuation of output 1 is slow. It will look like Figure 3 (bl).

On the other hand, in the case of FIG. 3 (al) of the embodiment, the switch S.

As soon as Qt is turned off, the resistance of C4 becomes smaller as Qt is turned on, so the rise of output 1 is faster than output 2, and no problem occurs.

(Effects) The present invention is as described above, and according to the multi-output switching regulator according to the present invention, the cutoff of the input power supply is detected, and the output smoothes at least one of the plurality of outputs. Since the electric charge in the power supply capacitor can be forcibly discharged, it is possible to force a fall between each output, so that it is possible to prevent a malfunction of a device using this power supply device when the power is turned off.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a multi-output switching regulator according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional multi-output switching regulator, and FIG.
) is a characteristic diagram of output 1 and output 2 according to the present invention and a conventional example.

Claims (1)

[Claims] A switching element that rectifies and smoothes an AC input power source to convert it into DC, one end of the DC output is connected to one end of a primary winding of a transformer having a plurality of secondary windings, and the other end is connected in series with the primary winding. By connecting the switching element to the other end and turning on and off the switching element, the voltage induced in each secondary winding is rectified and smoothed, and multiple DC outputs are obtained.
In a multi-output switching regulator that obtains a plurality of stable outputs by comparing one signal with a reference value and controlling the on/off of the switching element, a cutoff of the AC input power source is detected, and at least one of the detected signals is detected. A multi-output switching regulator characterized by forcibly discharging the charge of a DC output smoothing capacitor.